Realex RealVault provides an XML API which you can use on your website to register a payer (person who is to make payment on your website), payment method (payment details of the person who is to make payment on your website), authorize payment transaction and then raise a manual transaction from a receipt-in (or deduct payment from an earlier authorized amount).
This integration allows the customer to remain on your website while making payment for the services/products he is purchasing from your website. The only thing you need to make sure is that you have a SSL certificate installed on your website as the customer would be entering his credit card details to proceed with the transaction.
I can integrate your website with Realex RealVault XML API so that you can start accepting payments online. Please contact me for further details